media: media-device: fix infoleak in ioctl media_enum_entities()

commit e6a623460e5fc960ac3ee9f946d3106233fd28d8 upstream.

This fixes CVE-2014-1739.

Signed-off-by: Salva Peiró <speiro@ai2.upv.es>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>